1. Field of the Invention
The present invention relates to a method of detecting a moving velocity (called velocity concerning movement of a cardiac paries or the like) of a tissue or a moving velocity (called blood flow rate) of blood, which is capable of preventing a detected moving velocity from being brought to a value larger than a true velocity and to an ultrasonic diagnosing apparatus using the method.
2. Description of the Related Art
FIG. 4 is a block diagram showing one example of a conventional ultrasonic diagnosing apparatus.
The ultrasonic diagnosing apparatus 500 transmits a series of plural ultrasonic pulses to the inside of a living body at time intervals T in a plurality of directions and receives an ultrasonic echo signal from within the living body while placing an ultrasonic probe 1 on the surface of the living body. The ultrasonic echo signal received by the ultrasonic probe 1 is inputted to a quadrature detector 4 through a transmitter-receiver 2.
The quadrature detector 4 multiplies a reference signal generated from a reference signal generator 3 by the ultrasonic echo signal so as to output an in-phase component I (In-Phase) and a quadrature component Q (Quadrature) therefrom.
Each of A/D converters 5 and 6 performs A/D conversion on the in-phase component I and the quadrature component Q.
When a moving velocity of a tissue from the living body is detected, switches 7a and 8b are respectively changed over to sides indicated by solid lines in FIG. 4 so that the in-phase component I and the quadrature component Q both subjected to the A/D conversion are inputted to an auto-correlator 9 without passing through MTI (Moving Target Indication) filters 7 and 8. On the other hand, when a moving velocity of blood is detected, the switches 7a and 8b are respectively changed over to sides indicated by dotted lines in FIG. 4 so that the in-phase component I and the quadrature component Q both subjected to the A/D conversion are inputted to their corresponding MTI filters 7 and 8.
The MTI filters 7 and 8 respectively eliminate unnecessary components (low-frequency components produced from tissues such as a cardiac paries whose moving velocity is relatively low) from the in-phase component I and the quadrature component Q and input the so-processed components to the auto-correlator 9.
A multiplier 9c of the auto-correlator 9 multiplies a quadrature component Qi corresponding to an i(=2, 3, . . . )th pulse of the plurality of ultrasonic pulses by a quadrature component Qi-1 corresponding to an (i-1)th pulse and outputted from a delayer 9a with a time delay and outputs the result of multiplication Qi.multidot.Qi-1 therefrom. Similarly, a multiplier 9d multiplies an in-phase component Ii by the quadrature component Qi-1 and outputs the result of multiplication Ii.multidot.Qi-1 therefrom. Similarly as well, a multiplier 9e multiplies the quadrature component Qi by an in-phase component Ii-1 generated from a delayer 9b with a time delay and outputs the result of multiplication Qi.multidot.Ii-1 therefrom. Further, a multiplier 9g multiplies the in-phase component Ii by the in-phase component Ii-1 and outputs the result of multiplication Ii.multidot.Ii-1 therefrom.
An adder 9h adds the output Qi.multidot.Qi-1 of the multiplier 9c to the output Ii.multidot.Ii-1 of the multiplier 9g and sends the result of multiplication corresponding to a real-part component (=Ii.multidot.Ii-1+Qi.multidot.Qi-1) to an average arithmetic device 9p. The average arithmetic device 9p performs average operation on real-part components Rei relative to all the i and supplies the resultant average real-part component Re to a velocity detector 12.
On the other hand, a subtracter 9k subtracts the output Ii.multidot.Qi-1 of the multiplier 9d from the output Qi.multidot.Ii-1 of the multiplier 9e and outputs the result of subtraction corresponding to an imaginary-part component Imi (=Qi.multidot.Ii-1-Ii.multidot.Qi-1) to an average arithmetic device 9q. The average arithmetic device 9q performs average operation on imaginary-part components Imi relative to all the i and outputs the resultant average imaginary-part component Im to the velocity detector 12.
The velocity detector 12 calculates a velocity v from the following equation: EQU v=k.multidot.tan-1(Im/Re)
(where k=c/(4.pi..multidot.fo.multidot.T)
c: velocity of ultrasonic wave in living body PA1 fo: frequency of transmitted ultrasonic wave PA1 T: pulse repetitive interval T=2d/c PA1 d: diagnosis distance)
The velocity v represents the moving velocity of the tissue or blood and is inputted to a DSC 13.
The ultrasonic echo signal received by the ultrasonic probe 1 is inputted to a B mode processor 15 through the transmitter-receiver 2 separately from the above-described ultrasonic echo signal.
The B mode processor 15 generates B mode image data, based on the ultrasonic echo signal and inputs it to the DSC 13.
The DSC 13 generates data about a colored image obtained by superposing an image produced by color-coding the tissue or blood moving velocity and a B mode image on one another from the velocity v and the B mode image data.
A CRT 14 displays the colored image on a screen thereof based on the color image data.
FIG. 5 is a conceptual view for describing a relationship between a real-part component Re, an imaginary-part component Im, a velocity v and a power P.
An angle tan-1 (Im/Re) of a vector (Re, Im) on complex coordinates represents the velocity v and a magnitude={Re2+Im2} represents the power P. Namely, the velocity v does not depend on the power P.
Thus, the relationship between a velocity Vb detected by the ultrasonic diagnosing apparatus 500 and a power P is represented as shown in FIG. 6. The detected velocity Vb depends upon the power P and is brought to an improper or irregular value much different from a true velocity v when the power P is lowered.
It is considered that this reason is because since unintended vectors Na and Ni produced due to noise or the like are added to an intended vector (Re, Im) and the unintended vectors are undefined as indicated by a circle NC as shown in FIG. 7, the detected velocity Vb is brought to a irregular or improper value but the range of its irregularity is brought to several times the true velocity v when the power P is low.
However, a problem arises that when the detected velocity Vb is larger than the true velocity v, the tissue or the flow of blood looks improper. A further problem arises that a color flow image unseemly comes into sight due to coloring of the image to no purpose.